Re: [RFC PATCH] membarrier: riscv: Provide core serializing command

From: Andrea Parri
Date: Thu Aug 03 2023 - 20:17:15 EST

> Can you double-check that riscv switch_mm() implies a fence.i or equivalent
> on the CPU doing the switch_mm ?

AFAICT, (riscv) switch_mm() does not guarantee that.

> AFAIR membarrier use of sync_core_before_usermode relies on switch_mm
> issuing a core serializing instruction.

I see. Thanks for the clarification.

BTW, the comment in __schedule() suggests that membarrier also relies on
switch_mm() issuing a full memory barrier: I don't think this holds.

Removing the "deferred icache flush" logic in switch_mm() - in favour of
a "plain" MB; FENCE.I - would meet both of these requirements.

Other ideas?